The present invention is directed to an insulating means for optical insulation of components which are integrated on a substrate for integrated optics. The invention is also directed to a method for making the insulating means.
Integrated optical components on an InP substrate are considered cost beneficial for optical communication transmission because planar technology replaces micro optics and micro mechanics. However, as a consequence of integration, the interaction between the individual components increases so that an undesired cross-talk arises between various transmission channels. Integration is therefore meaningful only to the extent to which one succeeds in realizing component structures with a high cross-talk attenuation.
Semi-insulating substrates, separating trenches and, in addition, shielding electrodes have been used for improving the electrical cross-talk attenuation for epitaxially grown components. Measures have also been undertaken against optical cross-talk in integrated optics. Light absorbing InGaAs layers are sometimes used for this purpose on substrates of InP. An example of this is disclosed in an article by Bornholdt et al "WAVEGUIDE-INTEGRATED PIN PHOTODIODE ON InP", Electronics Letters, Vol. 23, No. 1, 2nd January 1987, pp. 2-4. The layer of thickness needed for complete absorption cannot be realized with the standard epitaxial method. Since the scattered light is uniformly distributed by multiple reflections in the crystal due to a high refractive index, individual separating trenches also seem rather unpromising.